Paddock, Zachary Dean (2010-08). Energy Expenditure in Growing Heifers with Divergent Residual Feed Intake Phenotypes. Effects and Interaction of Metaphylactic Treatment and Temperament on Receiving Steers. Master's Thesis. Thesis uri icon

abstract

  • Cattle classified as having low residual feed intake (RFI) phenotypes are those that consume less feed than expected based on body weight and growth performance. Mechanisms contributing to the variation in RFI are not fully understood. Previous studies have shown that cattle of divergent RFI phenotypes have different levels of energy expenditures, which are associated with heat increment, basal metabolism, thermoregulation responses, and physical activity. The objectives of this experiment were to characterize residual feed intake (RFI) in growing heifers and to determine if variation in whole-animal energy expenditure contributes to differences in RFI. Brangus heifers (n =120) were individually fed a roughage-based diet (1.93 Mcal ME/kg DM) diet twice daily and feed refusals measured weekly. Heifers were weighed once weekly for 70 d and RFI calculated as the difference between actual and expected DMI from linear regression of DMI on ADG and mid-test BW0.75. Immediately following the 70 d study, oxygen pulse rate (mL O2/heart beat) and 48-h heart rates were measured on 8 high and 8 low RFI heifers to estimate energy expenditure. Daily heart rates and oxygen pulse rates were higher (P < 0.05) in heifers with high RFI compared to those with low RFI. As a result, energy expenditure (kcal/BW0.75) was estimated to be 17.4 percent greater (P < 0.05) in high-RFI heifers then low-RFI heifers. Mortality and morbidity losses caused by bovine respiratory disease (BRD) continue to negatively impact the net revenues of the beef cattle industry. Stress can predispose calves arriving at feedlots to BRD by impairing their immune system with calves having more excitable temperaments possibly having a greater risk. The objectives of the second study was to examine the effects of metaphylactic treatment and temperament on performance, feed intake, feed efficiency, and feeding behavior traits in steers. Santa Gertrudis steers (n =119) were weighed and randomly to control (CON; no antimicrobial treatment) or metaphylactic (MET; 1.5 mL/45 kg BW of ceftiofur crystalline free acid) treatments. Steers were weighed at 14-d intervals and individual intakes and feeding behavior traits measured using a GrowSafe sytems while fed a roughage-based diet (2.21 Mcal ME/kg DM). Objective (relative exit velocity; REV) and subjective (chute score; CS) measurements of temperament were measured on arrival and on day 28 of the study. Steers with higher REV weighed less, grew slower, consumed less feed, spent less time consuming feeding, had more feeding bouts per meal, had less backfat, smaller longissimus muscle area, and higher cortisol levels. Steers treated with MET had higher ADG than those receiving CON. Cattle with higher REV that received MET had less of a decrease in ADG, DMI, time spend consuming feed, and less of an increase in feeding bouts compared to high REV steers receiving CON. Results from this study suggest that process-control strategies, which quantify and manage inter-animal variation in calf temperament may facilitate more judicious use of antimicrobial products and provide more consistent and predictable responses to metaphylactic strategies.
  • Cattle classified as having low residual feed intake (RFI) phenotypes are those that

    consume less feed than expected based on body weight and growth performance. Mechanisms

    contributing to the variation in RFI are not fully understood. Previous studies have shown that

    cattle of divergent RFI phenotypes have different levels of energy expenditures, which are

    associated with heat increment, basal metabolism, thermoregulation responses, and physical

    activity. The objectives of this experiment were to characterize residual feed intake (RFI) in

    growing heifers and to determine if variation in whole-animal energy expenditure contributes to

    differences in RFI. Brangus heifers (n =120) were individually fed a roughage-based diet (1.93

    Mcal ME/kg DM) diet twice daily and feed refusals measured weekly. Heifers were weighed

    once weekly for 70 d and RFI calculated as the difference between actual and expected DMI from

    linear regression of DMI on ADG and mid-test BW0.75. Immediately following the 70 d study,

    oxygen pulse rate (mL O2/heart beat) and 48-h heart rates were measured on 8 high and 8 low

    RFI heifers to estimate energy expenditure. Daily heart rates and oxygen pulse rates were higher

    (P < 0.05) in heifers with high RFI compared to those with low RFI. As a result, energy

    expenditure (kcal/BW0.75) was estimated to be 17.4 percent greater (P < 0.05) in high-RFI heifers then

    low-RFI heifers.

    Mortality and morbidity losses caused by bovine respiratory disease (BRD) continue to

    negatively impact the net revenues of the beef cattle industry. Stress can predispose calves

    arriving at feedlots to BRD by impairing their immune system with calves having more excitable

    temperaments possibly having a greater risk. The objectives of the second study was to examine the effects of metaphylactic treatment and temperament on performance, feed intake, feed

    efficiency, and feeding behavior traits in steers. Santa Gertrudis steers (n =119) were weighed

    and randomly to control (CON; no antimicrobial treatment) or metaphylactic (MET; 1.5 mL/45

    kg BW of ceftiofur crystalline free acid) treatments. Steers were weighed at 14-d intervals and

    individual intakes and feeding behavior traits measured using a GrowSafe sytems while fed a

    roughage-based diet (2.21 Mcal ME/kg DM). Objective (relative exit velocity; REV) and

    subjective (chute score; CS) measurements of temperament were measured on arrival and on day

    28 of the study. Steers with higher REV weighed less, grew slower, consumed less feed, spent

    less time consuming feeding, had more feeding bouts per meal, had less backfat, smaller

    longissimus muscle area, and higher cortisol levels. Steers treated with MET had higher ADG

    than those receiving CON. Cattle with higher REV that received MET had less of a decrease in

    ADG, DMI, time spend consuming feed, and less of an increase in feeding bouts compared to

    high REV steers receiving CON. Results from this study suggest that process-control strategies,

    which quantify and manage inter-animal variation in calf temperament may facilitate more

    judicious use of antimicrobial products and provide more consistent and predictable responses to

    metaphylactic strategies.

publication date

  • August 2010